The structure and assembley of the outer membrane of E.coli is being studied. The insertion of newly-synthesized lipopolysaccharide occurs at 20-50 insertion points in this membrane, from which it spreads througout the membrane. Studies using electron spin resonance techniques to analyze the fluidity of this membrane have shown that it is very rigid, relative to other membranes, and that the reigidity is reduced if either the length of the lipopolysaccharide carbohydrate moiety, or the absolute amount of lipopolysaccharide, is reduced. These results indicate that lipopolysaccharide is directly or indirectly responsible for the rigidity of this membrane. A new transducing phage has been characterized in the E.coli strain, 0111:B4. The relationship of this phage to other known transducing phages is being studied.